if one truly 'understands' what they are doing, then they are in the Will of God, but,
if they don't have a clue other than just 'getting-wet', following the crowd, then
of course it is of no profit, only grief...
been there, got that Tee-Shirt as a teen, with ever so many regrets before
witnessing the Holy-True-Light so many years later...
Truely understands? I don't understand this, there are so many Christians, I would say especially in western culture that have only a very vapid level of understanding of what baptism is. Does understanding change who, God is or his promise?
Did the Ethiopian eunuch full understand baptism? From every account written in acts they baptized folks immediately upon believing in Jesus.
Why do we make things so complicated? If you notice the letter to the Romans an explanation is given to the believers, because they didn't understand, yet were baptized. We need to baptize everyone who believes without hesitation. A short synopsis should be offered and into the water.
You could offer the explanation as a baptismal sermon while you baptize if you felt it needed be.
We create to much doubt in folks mind by being overly tedious about the Gospel of truth.
So many times folks tell me they don't know of they are saved. I have two questions for that person. Do you believe in the Lord Jesus Christ? Is they answer yes, I follow with are you baptized. If they say yes, I say you are indeed saved and a Christian, If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
1 John 1:9 KJV
https://bible.com/bible/1/1jn.1.9.KJV
So confess them to him now and have faith.
If they answer either of the questions, no, then I work with them to rectify that.